Recently, scientists have been developing alternative ultra-high-density data storage devices and techniques useful for operating ultra-high-density data storage devices. These devices and techniques store data bits within storage areas sized on the nanometer scale and possess advantages over conventional data storage devices. Among these advantages are quicker access to the data bits, a lower cost per bit and enablement of the manufacturing of smaller electronic devices.
FIG. 1 illustrates an ultra-high-density data storage device configuration according to the related art that includes a storage medium 40 that is separated into many storage areas (illustrated as squares on the storage medium 40), each capable of storing one data bit. Two types of storage areas, unmodified regions 140 that typically store data bits representing the value “0” and modified regions 130 that typically store data bits representing the value “1”, are illustrated in FIG. 1. Typical periodicities between any two storage areas in these devices range between 1 and 100 nanometers.
FIG. 1 also shows, conceptually, emitters 350 positioned above the storage medium 40, and a gap between the emitters 350 and the storage medium 40. The emitters 350 are capable of emitting electron beams and are arranged on a movable emitter array support 360 (also known as a “micromover”) that can hold hundreds or even thousands of emitters 350 in a parallel configuration. The emitter array support 360 provides electrical connections to each emitter 350 as illustrated conceptually by the wires on the top surface of emitter array support 360.
The emitter array support 360 can move the emitters 350 with respect to the storage medium 40, thereby allowing each emitter 350 to scan across many storage areas on the storage medium 40. The storage medium 40 can also be placed on a platform that moves the storage medium 40 relative to the emitter array support 360. The platform can be actuated electrostatically, magnetically or by the use of piezoelectrics and, dependent upon the range of motion between the emitter array support 360 relative to the storage medium 40, each emitter 350 can have access to data bits in tens of thousands or even millions of data storage areas.
Related Art: (Ultra-High Density Data Storage Devices)
Some specific embodiments of the ultra-high-density data storage device discussed above are disclosed in U.S. Pat. No. 5,557,596 to Gibson et al. (Gibson '596), the contents of which are incorporated herein in their entirety by reference.
The devices disclosed in the Gibson '596 patent include a storage medium 40 with modified regions 130 and unmodified regions 140, emitters 350 and an emitter array support 360. The Gibson '596 devices provide a relatively inexpensive and convenient method for producing ultra-high-density data storage devices that can be manufactured by well-established and readily-available semiconductor processing technology and techniques. Further, some of the devices disclosed in the Gibson '596 patent are somewhat insensitive to emitter noise and variations in the gap distance between the emitters 350 and the storage medium 40 that may occur when the emitters 350 move relative to the storage medium 40 during device operation. Reasons for these insentivities are related, for example, to the nature of the diode devices disclosed in the Gibson '596 because the diodes allow constant current sources to be connected to the emitters 350 and allow the electron beam energy to be monitored independently of the signal current in order to normalize the signal as described in the Gibson '596 patent. However, the devices disclosed in the Gibson '596 patent must be operated under stringent vacuum conditions.
The storage medium 40, according to the Gibson '596 patent, can be implemented in several forms. For example, the storage medium 40 can be based on diodes such as p-n junctions or Schottky barriers. Further, the storage medium 40 can include combinations of a photodiode and a fluorescent layer such as zinc oxide. This type of configuration relies on monitoring changes in the cathodoluminescence of the storage medium 40 to detect the state of a written bit. Also, according to the Gibson '596 patent, the storage medium 40 can be held at a different potential than the emitters 350 in order to accelerate or decelerate electrons emanating from the emitters 350.
The emitters 350 disclosed in the Gibson '596 patent are electron-emitting field emitters made by semiconductor micro-fabrication techniques and emit very narrow electron beams. These can be silicon field emitters but can also be Spindt emitters that typically include molybdenum cone emitters, corresponding gates and a pre-selected potential difference applied between each emitter and its corresponding gate. The Gibson '596 patent also discloses electrostatic deflectors that sometimes are used to deflect the electron beams coming from the emitters 350.
According to the Gibson '596 patent, the emitter array support 360 can include a 100×100 emitter 350 array with an emitter 350 pitch of 50 micrometers in both the X- and Y-directions. The emitter array support 360, like the emitters 350, can be manufactured by standard, cost-effective, semiconductor micro-fabrication techniques. Further, since the range of movement of the emitter array support 360 can be as much as 50 micrometers, each emitter 350 can be positioned over any of tens of thousands to hundreds of millions of storage areas. Also, the emitter array support 360 can address all of the emitters 350 simultaneously or can address them in a multiplex manner.
During operation, the emitters 350 are scanned over many storage areas by the emitter array support 360 and, once over a desired storage area, an emitter 350 can be operated to bombard the storage area with either a high-power-density electron beam or a low-power-density electron beam. As the gap between the emitters 350 and the storage medium 40 widens, the spot size of the electron beams also tends to widen. However, the emitters 350 must produce electron beams narrow enough to interact with a single storage area. Therefore, it is sometimes necessary to incorporate electron optics, often requiring more complicated and expensive manufacturing techniques to focus the electron beams.
If the emitters 350 bombard the storage areas with electron beams of sufficient power density, the beams effectively write to the storage medium 40 and change the bombarded storage areas from unmodified areas 140 to modified areas 130. This writing occurs when electrons from the high-power-density-electron beams bombard the storage areas and cause the bombarded storage areas to experience changes of state such as changes from crystalline structures to amorphous structures or from undamaged to thermally damaged.
The changes of state can be caused by the bombarding electrons themselves, specifically when collisions between the electrons and the media atoms rearrange the atoms, but can also be caused by the high-power-density-electron beams transferring the energy of the electrons to the storage areas and causing localized heating. For phase changes between crystalline and amorphous states, if a rapid cooling process follows the heating, an amorphous state is achieved. Conversely, an amorphous state can be rendered crystalline by heating the bombarded storage areas enough to anneal them.
The above writing process is preferable when the storage medium 40 chosen contains storage areas that can change between a crystalline and amorphous structure and where the change causes associated changes in the material's properties. For example, the electrical properties, crystallography, secondary electron emission coefficient (SEEC) and backscattered electron coefficient (BEC) can be altered. According to the devices disclosed in the Gibson '596 patent, these changes in material properties can be detected and allow for read operations to be performed, as will be discussed below.
When a diode is used as the storage medium 40, high-power-density bombarding beams locally alter storage areas on the diode surface between crystalline and amorphous states. The fact that amorphous and crystalline materials have different electronic properties is relied upon to allow the performance of a read operation, as will be discussed further below.
When writing to a storage medium 40 made up of a photodiode and a fluorescent material, the emitters 350 bombard and alter the state of regions of the fluorescent material with the high-power-density-electron beams. This bombardment locally alters the rates of radiative and non-radiative recombination and, thereby, locally alters the light-emitting properties of the bombarded regions of the fluorescent layer and allows yet another approach, to be discussed below, for performing a read operation.
Once data bits have been written to the storage medium 40, a read process can retrieve the stored data. In comparison to the high-power-density-electron beams used in the write process, the read process utilizes lower-power-density-electron beams to bombard the storage regions on the storage medium 40. The lower-power-density-electron beams do not alter the state of the storage areas they bombard but instead either are altered by the storage medium 40 or generate signal currents therein. The amplitudes of these beam alterations or signal currents depend on the states of the storage areas (e.g., crystalline or amorphous) and change sharply dependent on whether the storage areas being bombarded are modified regions 130 or unmodified regions 140.
When performing a read operation on a storage medium 40 that has storage areas that can change between a crystalline and amorphous structure and where the change causes associated changes in the material's properties, the signal current can take the form of a backscattered or secondary electron emission current made up of electrons collected by a detector removed from the storage medium. Since SEEC and BEC coefficients of amorphous and crystalline materials are different, the intensity of the current collected by the detector changes dependent on whether the lower-power-density-electron beam is bombarding a modified region 130 or an unmodified region 140. By monitoring this difference, a determination can be made concerning whether the bombarded storage area corresponds to a “1” or a “0” data bit.
When a diode is chosen as the storage medium 40, the signal current generated is made up of minority carriers that are formed when the lower-power-density electron beam bombards a storage area and excites electron-hole pairs. This type of signal current is specifically made up of those formed minority carriers that are capable of migrating across the interface of the diode and of being measured as a current. Since the number of minority carriers generated and capable of migrating across the diode interface can be strongly influenced by the crystal structure of the material, tracking the relative magnitude of the signal current as the beam bombards different storage areas allows for a determination to be made concerning whether the lower-power-density-electron beam is bombarding a modified region 130 or an unmodified region 140.
In the case of a photodiode and fluorescent material used as the storage medium 40, the lower-power-density electron beam used for reading stimulates photon emission from the fluorescent material. Dependent on whether the region bombarded is a modified region 130 (e.g., thermally modified) or an unmodified region 140, the number of photons stimulated in the fluorescent material and collected by the photodiode will be significantly different. This leads to a different amount of minority carriers generated in the photodiode by the stimulated photons and results in a difference in the magnitude of the signal current traveling across the photodiode interface as the beam bombards different storage areas.
In many of the embodiments described above, a bulk-erase operation is possible to reset all of the modified regions 130 present on the storage medium 40 after the writing process. For example, if an entire semiconductor storage medium 40 is properly heated and cooled, the entire storage medium 40 can be reset to its initial crystalline or amorphous structure, effectively erasing the written data bits. With regard to a photodiode storage medium 40, bulk thermal processing can reset thermally altered areas by processes such as annealing.
Related Art: Atomic Force Microscopes (AFM)
FIG. 2 illustrates a top view of a typical AFM probe 10 according to the related art that is made up of a tip 20, a compliant suspension 30 that supports the tip 20 and that itself is supported by other components of the AFM (not shown) and a piezoelectric material 50 deposited on the top surface of the compliant suspension 30.
The probe 10 can be operated in the contact, non-contact or tapping (intermittent contact) AFM modes that are well known in the art and that will only briefly be discussed here. The contact mode allows for direct contact between the tip 20 and the storage medium 40 while the non-contact mode (not shown) keeps the tip 20 in close proximity (generally on the order of or less than approximately 100 nanometers) to the storage medium 40. The tapping mode allows the compliant suspension 30 to oscillate in a direction perpendicular to the surface of the storage medium 40 while the probe 10 moves in a direction parallel relative to the storage medium 40 and the tip 20 therefore contacts or nearly contacts the storage medium 40 on an intermittent basis and moves between positions that are in direct contact with and in close proximity to the storage medium 40.
The tip 20 is typically, although not exclusively, made from silicon or silicon compounds according to common semiconductor manufacturing techniques. Although the tip 20 is typically used to measure the dimensions of surface features on a substrate such as the storage medium 40 discussed above, the tip 20 can also be used to measure the electrical properties of the storage medium 40.
As stated above, the tip 20 in FIG. 2 is affixed to a compliant suspension 30 that is sufficiently flexible to oscillate as required by the intermittent contact or tapping mode or as required to accommodate unwanted, non-parallel motion of the tip suspension with respect to the storage medium during scanning (so as to keep the tip in contact or at the appropriate working distance). The compliant suspension 30 typically holds the tip 20 at one end and is attached to and supported by the remainder of the AFM or STM structure on the other end. Storage medium 40, in a typical AFM structure, rests on a platform that is moved with relation to the tip 20, allowing the tip 20 to scan across the storage medium 40 as the platform moves.
FIG. 2 illustrates a piezoelectric material 50 deposited on the top surface of the compliant suspension 30. As the tip 20 moves across the storage medium 40, the tip 20 moves the compliant suspension 30 up and down according to the surface variations on the storage medium 40. This movement, in turn, causes either compression or stretching of the piezoelectric material 50 and causes a current to flow therein or causes a detectable voltage change. This voltage or current is monitored by a sensor (not shown) and is processed by other components of the AFM or STM to produce images of the surface topography of the scanned area.
Disadvantages of the Related Technology.
Typical ultra-high-density data storage devices, the devices disclosed by the Gibson '596 patent and the AFM devices described above have several shortcomings for producing high-density data storage devices.
Among the limiting factors of the emitter-based devices disclosed above is the dependency of the spot size of the bombarding beam on the distance separating the emitters 350 and the storage medium 40. This dependency results from the fact that beams emitted by the emitters 350 have a tendency to spread proportionally to the distance that they travel before bombarding the storage medium 40.
Another limitation of the emitter-based devices described above is the vacuum requirement that must be satisfied in order to perform the read and write operations. Without the appropriate vacuum conditions being attained, the beams emitted by the emitters 350 interact with particles present between the storage medium 40 and the emitters 350 and do not reach the storage medium 40 in a sufficiently focused state to perform read and write operations. A poor vacuum can also cause unstable emission and even arcing, which can damage the emitter 350. It can also shorten the emitter 350 or storage medium 40 lifetime via ionization of gas molecules followed by ion bombardment, or via reaction of the emitter 350 or storage medium 40 with gas molecules (particularly ionized ones).
A disadvantage common to all devices described above is emitter damage, in the form of either wear or breakage, that becomes a concern when the emitters 350 contact the storage medium 40. Such contact can occur when the storage medium 40 contains a large topographical feature on the surface thereof that an emitter 350 collides with as the emitter 350 scans across an array of storage areas. Such contact also occurs when an AFM tip 20 is used to read repeatedly from storage medium 40 in contact or intermittent contact modes, thereby wearing the tip 20 and the storage medium 40 over time.
Therefore, what is needed is a method of reading data from and writing data to a storage medium 40 that allows for the focusing of a very small beam spot on the storage medium 40.
What is further needed is a method for energy-beam emitters 350 and tips 20 to be self-forming and/or self-repairing.
What is also needed is a method of reading from and writing to a data storage medium 40 that alleviates or eliminates the necessity for a vacuum environment.